You're happily working at your table saw. Unfortunately the nearby motion sensor has been covered in saw dust. The system does not detect any motion and turns off the lights. Plop. Your severed hand falls to the floor.

In a shop, a human brain needs to be responsible for turning off the lights.

I see your point, what I do creates a ton of dust not sawdust but concrete dust the kind that destroys everything and gets everywhere.

I was also thinking of some sort of RFID access and sensors... BUT all that does add to the cost and complexity and in the end I may just have switches. I still would like to be able to individually dim and control each light as opposed to all on one switch.

The other reason I liked the presence sensing options is that I do not need to coat the switches with concrete each time I try to control something.

That makes sense. Whatever it will turn out to be, you can control the lights from one central location.If you make the lights with light sensors (I would choose ldr) and motion detectors, you can make the central unit as complex or as simple as you would like.

You could add a current clamp over the mains wire, to see if any electrical machine is on.Adding a remote control would be nice.And sending a detection alert to a sms or website, as a burglar alert.

Im using a CAt kit and kitten board to run high power LED lights in my greenhouses, The distance from the leonardo is about 25Metres. It really made setting up the system simple and it has been reliable. Im a fan- (it runs fans too on some of the other pins)

I got a CATkit and 3 kittens 3 weeks ago. Connecting everything was a breeze. The Arduino itself sits in my office with the CATkit shield attached. I'm running 30ft and 75ft CAT5 cables out to 2 kittens with sensors along a busy traffic lane in the warehouse to the loading doors. These are connected to a kitten each with a 4 channel relay that hooks to a mains powered LED light bar. I suppose plugging PIR sensors into kittens to control the the light relay would be the same idea. These are currently running on the digital pins monitoring traffic and the door activity - when a door is opened (contact switch) I sound a piezo buzzer and turn on the loading bay lights. The third kitten is running an LCD display showing the door open/closed status. This uses SPI over the analog pins.

The CATkit was pretty easy to put together and the pins were straightforward to work with. The other option I was considering to assemble the whole system was wireless, but the CATkit did the job for much cheaper and connectivity/distance/interference hasn't been an issue yet. I've got room on the kittens and plans to get creative and start adding automatic PIR light controllers for the rest of the warehouse. The intention behind this is to turn off the lights when they are not needed in the rest of the warehouse. Its been a neat project and I'm hooked on the arduino now! Looks like I need to upgrade to a Mega soon.